Conventional methods for analyzing stress in an object with photoelasticity involve complex computing algorithms for converting wrapped phases, which are constrained in either an interval of (−π, π] or an interval of [0,2π), into unwrapped phases. Generally, a spatial phase unwrapping algorithm or a temporal phase unwrapping algorithm can be used to convert the wrapped phases into the unwrapped phases in the conventional methods for stress analysis. However, conversion of the wrapped phases into the unwrapped phases demands lots of computing resources and time since the algorithms involve modulo operation on the wrapped phases (e.g., π modulo and 2π modulo). Another conventional method for stress analysis in an object is an iterative method. However, the iterative method compares spectrum data of the object with a mass of spectrum data pre-stored in a database one by one, which requires a considerable amount of time and thus reduces overall efficiency.
Furthermore, light rays used in photoelasticity to generate spectrum data for stress analysis must have different wavelengths λ1, λ2, λ3. The wavelengths λ1, λ2, λ3 must satisfy a specific condition
            λ      2        =                            λ          1                ⁢                  λ          3                                      λ          1                +                  λ          3                      ,            λ      1        >          λ      2        >                  λ        3            .      